Quoted for emphasis. Find out who's paying your bill...spend your taxpayer-alloyed funds wisely...especially if your TDY is unit funded. Talk to your unit FM or DTS or "TDY orders" guy and see what's "standard" for your unit--if it's jiggy with the JFTR, just do that.
I once agreed to let a guy PCS in then go unit-funded O&B TDY to training. I allocated $7K for the month's rental car, airfare, and on-base perdiem and lodging. He spent the month off-base and spent a LOT more, legally, but without our knowledge, and royally pissed off the commander before he'd even met the guy. We paid his bill, of course, but were then unable to accomplish 3-4 other TDYs that year....
Technique only.